Ultrahigh-frequency pulse oscillator



Nov- 13, 19 1 s. TESZNER 2,575,200.

Y ULTRAHIGH-FREQUENCY PULSE OSCILLATOR Filed Jan. 21, 1948 sSheets-Sheet 1 "nun LOAD VOLTAGE I Fi .2

CURRENT Fi 3 I Fig. 4

I, VOLT/155 CURRENT ZA/VE VT 5 71 4 1-5445 /6q=uv5&

Nov: 13, 1951 s. TESZNER 2,575,200

ULTRAHIGH-FREQUENCY PULSE OSCILLATOR Filed Jan. 21, 1948 5 Sheets-Sheet2 VOU'AGE TIME CURRENT I re/vra4 fnqA/nsLas 7;: 2. "El! Nov. 13, 1951 s.TESZNER 2,575,200

ULTRAHIGH-FREQUENCY PULSE OSCILLATOR Filed Jan. 21, 1948 3 Sheets-Sheet3 74 CLAY CONTAINING A CONDUCTOR CLAY CONTAINING A CONDUCTOR CLAYCONTAINING A CONDUCTOR Patented Nov. 13, v 1951 ULTRAHIGHJREQUENCYPULSE.

' OSCILLATOR StanislaszTeszner, Paris; France Application January 21,1948, Serial No. 3,650

InFranc'etJanuary '28, 1947 IOFCI'aiins;

f The object-of the-prescnt'inventiorris' a novel circuit for highfrequency pulse oscillators: moreespecially adapted to pulse-transmitters"- operat ing' at ultra high fiequenci'es corresponding towave *lengths oftheorder'ofmagnitude oi" a fewcentimetersor; atmost;-a-- fewdecimeters and wherein high frequency oscillating energy is produced in-theiorm of'puls'e'sfbf very snortdiiration; In my copendingapplication for patent of the" United? States;1SerialiNo; .3.;6"49;filed January: 21, 1948 entitled- Improvementsiain Modulators? for PulseTransmitters, I: have": disclosed improve ments in iriodulators';operating: through therapplication ofcompoundelectroniczsemifeconductors and I more: particularly through' theuse ofthe electric: hysteresis:- of: such. semi -conductorsF in order to--obtain'-"a-- desiredeshapaofr pulse: or. pip: My present invention.-has for its object theextension of v such an. application=to=oscillatorsfor pulse transmitters, according to.- which electrichysteresisis usedno-longen for the obtentiorrot a= desired shape of pip.butfon. ensuring? theoscilrlation of .the oscillatorsundenthebest.conditions of energy efficiency. I

This application is. of particular interestior veryhigh frequencysuchas, for waves. of L a few centimeters. or decimeters and for very.short. durations. of the pip for which theeffect of hysteresis may beeasily increased andiI held out during the major. part of.- the" whole"duration of the pip. The" said' phenomenon of electric hysteresis is initself known and" may also. he bettercall'd electric residual eflctl'Such=anosci11ator is constituted after' the manner of already knownspark oscillatorswl'ierein tlie'sparkgap is 'replacedbya compoundsystemof electronic" semi conductors arranged in ac cordancewith my invention:These'comp'ound electronic semi-conductors are"- constituted bysemiF-conductive grains for. instance- Caruorundum-grains; whiclras' 'arule are agglomerated by means of "an": auxiliary oompoundrsuclr asclay; the mixture: being baked at liighr temperature? Thisrnat'erial-ris characterizedfby a mo're"v or le'ss considerablevariation ofi. its conductivity: as": afunction ofthe-voltagjeappliedito the terminals: Moreover, in the case. of; ther presentinvention the: electric hysteresis is so extended that; during a'rise-of thervoltage of th'e:impulsio'ri'theicurrent practically doesnot-rise; whilerduringi a voltage drop it *rises abruptly: up: to". a1limit determined by the iinpedanceaoF-the oseillatoiy ciicuitxwhenthewhigh conductivityrofithe compound iss-m'ainrtainedr at least:during: the? greater part of? the" pulse duration.

2, It is true'that sp'arkgapshave allowed; quite recently; reachingconsiderable peak'powerswith metric waves" and on the" other handinvestigations, made some considerable time ago, have led'totheproductio'nof wavetrainsat extremely high frequencies butsjuchzwavetrainswere highly damped and provided only a small peak power.As amatterof fact; it" is*found"'that'when the frequency is raised moreparticularly above 10 periods per second; the phenomena of inertia ofthe spark become extremely troublesome: This inertia is both alongitudinal" inertia appearing in the formation ofth'e'spark andinitsrestriking witha'reversal offcurrentateach alternaricean'da'transvers'al inertia appearing'irrasm'uch as the area correspondingto' the: spark does riot" follow synchronously the variation in current.The two forms'o'finertia produce anincrease in' th'e'efiicient drop of"voltage in the" spark" andconsequently a rapid" damping of'theoscillation and a reduction in. theenerg'y 'performance:

To-reduce' inertia", itisappare'nt" that it is necessary to attempt onone'rhand" anincr'ease in the speed of displacement of the electronsthrough: an-increase in thefreepath ofth'e elec'- trons i. e. byaccelerating the move1herit'of'* the electrons through :an increase inthe gradient of otential in the striking'interval and'on the other handto reduce the cross=sectional area of the spark by increasing thedensity" of' the current Various contrivancesihavebeen proposedto saidpurpose. I

The use of a dielectric medium constituted. by compressed gas forincreasing the gradient 01 potential in: the striking intervaPtogetherwith the currentdensity'in the'sparkbut reducing the freedom of movement'of" electrons by; reason of the' reduction'in" the freepath"of"said"electrons; has allowed reachingrpeak powers that are con--siderable for metric waves; however" for" higher frequencies -of theorderof 10 andabove it seems that'such a' contrivance cannotlead toresults of any interest unless: practically prohibitive pres sures areresortedto:

Th'e're'duction of the'spacing"between electrodes to an intervalco'rrespondingtothe magnitude of the free travel of elctronsiundenatmospherio pressure constitutes theoretically" an excellentsolution" o'fi-f the problem; Unfortunately, this solutionappearspractically inapplicable; at least for high voltagesandiinten'seFcurrents by reason of the unavoidahleiformation of:conductive bridgesfbetween the; electrodes;

The user: of a high vacuum: asi a dielectric iiiedium seems also atflrst etc-interest; liut ifiin order to avoid any increase in thecathodic interval which would lead to a corresponding increase of thedrop of voltage with reference to that ob tained under atmosphericpressure, it would be necessary to limit the spacing of the electrodesto a magnitude corresponding to the cathodic interval under atmosphericpressure. This spacing of the electrodes although it is more importantthan in the preceding case would be still insuflicient for removing thenormal possibility of the formation of conductive bridges.

One is thus led to contemplate setting the electrodes permanently incontact, the contact thus provided having to be originally of highresistance and becoming as it were active with the conductivity risingsuddenly after the manner of a spark resistance through the applicationof a voltage of corresponding value. To allow the ap plication of such avoltage while avoiding parasitical external possibilities of striking,the contacts should be located inside a medium 'of'high dielectricrigidity, preferably a high vacuum, so as to further the electronicemission starting from the electrode when cold. However whatever may bethe medium used, it is hardly possible to obtain with a single contacthigh voltage nor to obtain the passage of intense currents. It would betherefore necessary to use a large number thereof in seriesand inparallel which leads to dimensions that are not acceptable for circuitsthat are to oscillate at very high frequencies.

Now acompound system of electronic semiconductors provides in practicesuch asystem of contacts but at a microscopic scale whereby the totalvolume occupied remains allowable in practice, even for applications tovery high frequencies.

However, it is apparent that if the characteristics of such a compoundcontact system are those generally sought for, to wit in the case ofincreasing currents the voltage does not drop, but holds out with aslight tendency to increase also, while electric hysteresis or residualelectric effeet is negl gible, the upward stroke for the voltage currentcurve under rising voltage conditions coinciding substantially with thereturn stroke for decreasing voltages, practically no oscillation may beinitiated by striking through the semi-conductor. For such anoscillation to be possible with an acceptacle energy efficiency it isnecessary that for an increasing current the voltage ultimately may dropconsiderably with a tendency to reach a predetermined lower limit and tostay there during a large part or even the totality of the duration ofthe pip; On the other hand to allow a loading of the capacity of theoscillating circuit the compound system of semi-conductors should notallow the passage of a substantial current ericept above a certain voltage near the amplitude of the loading voltage. These results may beobtained by using and extending to a maximum the electric hysteresis ofthe compound of semi-conductors in accordance with the object of theinvention; 1

' The above described features and advantages will be better understoodby the reading 'of the following description which discloses a fewexamples of diagrams of oscillating circuits including'a compoundsemi-conductor according to the invention, reference being had to thefollowing figures-of the drawings annexed to the specification andforming part thereof;

Fig. 1 is a diagram reduced to its simplest form of an oscillatoraccording to'this invention.

Figs. 2 and 5 show the impulse voltage current curves of semi-conductorsystems with different hysteresis efiects.

Figs. 3 and 6 show voltage-time curves across the terminals of saidsemi-conductors during the corresponding oscillations.

Figs. 4 and '7 are current-time curves for said correspondingoscillations.

Figs.'8, 9 and- 10 show diagrammatically different forms of the primaryoscillators.

The diagram of the oscillator (Fig. 1) comprises a source I shown by wayof example, as being a direct current supply, and a resistance,induction coil or the like impedance 2 adapted to load the condenser 3,forming the modulator in association with the spark gap 4 and the piptransformer 5 which latter may however be omitted. The diagram alsoincludes the so-called choke coil 6, the capacity 1, the induction coil8 and the compound system of electronic semiconductors 9 in the primarycircuit of the oscillator cooperating with the capacity II and theinduction coil I 0 of the secondary circuit coupled with the primarycircuit. The presence of a secondary circuit is however entirelyoptional and is only necessary when it is desired to extend the durationof the pips and also to reduce to a minimum the duration of thedischarge together with the dissipation of energy in the compoundsemiconductor 9.

The operation of such an oscillator is readily apparent. The condenser 3is loaded by the source I through the agency of the impedance 2. As soonas the desired voltage is reached, the spark gap 4 breaks down or elsethis breaking down is obtained through a synchronizing pulse and thevoltage considered is applied suddenly through the transformer 5 if sucha transformer is used, to the oscillating circuit so as to load suddenlythe capacity I. From this moment onwards, when a predetermined voltageacross the terminals of the latter is reached, the oscillation of theprimary circuit is initiated and is transmitted to the secondary circuitif such a circuit is used. v I r However, it has already been statedthat for a suitable loading of a circuit with a possibility of itsoscillation being developed thereafter and continuing with a good energyeificiency, it is necessary for the compound system of semi-conductorsto show an extremely high resistance up to a certain value of thevoltage and for said resistance to then collapse and keep a very lowvalue duringall or at least a-large part of the duration of thedischarge. I a

The oscillator may be energized'if the hysteresis has a considerablevalue, but only within the limits of each half-period. The oscillationscannot be developed except when conditions are favorable therefor. Itwill be seen by reference to the voltage-intensity curve of Figure 2, inwhich the arrows-show the direction of variation of the voltage, thatthe' compound semi-con ductor returns toits original characteristic eachtime the voltage andthe intensity pass through zero. The favorableconditions exist only during a period which isat best one quarter of aperiod for each half period. Referring to Figs. 3 and 4, Figure 3 ofwhich illustrates a first period of the voltage across the terminals ofthe semi-con ductor system and Fig. 4 of'which illustrates acorresponding first period of the current, itwill be seen that theoscillation is considerably damped; consequently the efficiencywillbe-mu'ch too small.

amazon But: if: such hysteresis; still remaining. impor= tant extendsover a considerable portion if not over. an: Whole duration? oi the pip;the: conditions are completely altered: The half periou or possibly thatwo first halfiper iodaltak ing into: account the two polarities} for-mto some extent; a period I of l formation for" the semi-conductor:compound after which by reason of the hysteresis, the internalresistance will remain very: small; fon'bothdirections': of the current.The'idamping' of? the discharge will be high' on'ly duringitheifirst or'thefirst two :half periods'I-a'fte'r which 'itl-is comparatively low;

Figs; 5, 6i and. '7 show respectively a? voltagecurrentlcurveiofithefcomp'ound semi con'ductor. as disclosed:hereinaboveraftera periodof formation shown: in" chain: lin'eit' extending. overltwoihalfperiods, the arrows illustrating the dir'ection of variationr: ofthe voltage; a: v'o1tage timecu'r ve acrossithe terminals of thecompound semi conductor'; and a current time curve. across; same thelatter 'curves beingshown': for *th'etwo first half periods and afewsucceeding half period's.

The: remarkable factisethus apparent that the hysteresis or residual.electric" efiect that" is extremely objectionable in the case of asparkzpl'ays in the present case a useful part; However it does not: actin practice as a' brake except dure in'githeinitiation period; producingas itwere: a storage: of energy for the subsequent releasero'fthe'idischargez- Subsequently, on the contrary; the very low internalinertia. appearingcb'y" reason of the microscopic size" of'i the'different insulating layeisoffthe semi cond'uctor system and also of thecomparatively considerable electric field prevailing therein, it's'eiiect producinga small equivalent resistance maybe kept-up during allor a large part of the duration of the Wave train and it may bementioned that the increase in the hysteresis'phenomenonismade easier"by the application of the loading voltages of the oscillator throughshocksby thebreakingidown of the spark gapA. asdisclosedwithreferenceito the'diag'r'am of Fig. 1*;

Such transmitters are capable of producing pips with peak powers thatare higher not only than those of pips produced by the spark gaptransmitters known to this day by reason of the comparatively very smalldrop in potential across the terminals of the energizing means but alsothan the power of the pips generated at the present time by thermo-ionictube transmitters. As a matter of fact, they are adapted to support muchhigher voltages and much more intense currents. To this purposearrangements should be taken to avoid any initiation through the outsideof the electronic semi-conductor compound, by locating the systemincluding the primary oscillator, inside a medium with a high dielectricrigidity, for instance in a high vacuum. On the other hand, as theenergy produced at each pip is a result of the energy stored during theloading of the primary oscillator, the structure of the latter should besuch that its electrostatic capacity may be as high as possible underconditions otherwise similar. Figs. 8, 9 and 10 show three forms ofexecution of such a circuit.

The circuit of Fig. 8 is a coaxial double quarter wave line constitutedby an inner lead I2 and an outer lead 13 between which the loadingvoltage is applied while the compound electronic semi-conductor I4 isdistributed annularly inside the central section of the circuit as shownin the drawing. Thus in the energization of this compound system therepasses a synchronous oscillationtiniboth halves .ofitheicircuit'aquarter wave type;

If it is possible to provide? foran uniform distributioniof'thefdischarge' in the. compound systern the: circuit: of: said: Fig; 8may assume a comparatively. large? transverse component and produceconsiderable: electrostatic: capacities and thereby.- considerablestored ienergy even for? extremelirhigh frequencies.

In the opposite case; his possible to prefer'cir cuitsfwhereinthecompound semi-conductor assumesa-mor'e compactshape. Thisis the case forinstance oftheispherical lune quarter wave circuitillustrated: in Fig, 9that" includes an interna1:lead1|5',: an outer lead lfiand a compoundsemi-conductor: fl at the apex or else of the circuit accordingito: Fig:10 with parallelplates I8 including atlth'e center thereof the compoundsemi-conductor 19 held between the two plates." It will be"noticedmoreover that thecircuit l s is am'ere development ona plane of thecircuit of Fig. 9 a'llowing an easierexecution thereof; Last- 1:the-"secondary'circuit, if present might'be constituted'for instance bya cavity resonator-coupled with the'primary-"through' any'n'ieans knownin thea'rtl The presence of the secondary circuit is particularly'o'finterest when it is clfesired to reach no'ti'only highpeakpowersforea'ch pip, but also high: mean powers.- As a" matter of fact} it isknownthat atight coupling b'etween'the primary and secondary allows aconsiderable" shortening ofitheduraticn of discharge of the primary andconsequentlyfor 'a same .mean power dissipated in theicomp'ound 'seni'iconductor, the rhythm of the pips" may be considerabl'y accelerated.

From :the' foregoing description .1 and function inglof the-compoundsemiconductor and from the description and 'useof l the samein thecop'ending application; it is obvious that different names c'anheappropriately applied to it, for ex ample,- it may'well be calledgranular semi-conductinglbody asifurthert advantages forthe-transmitters l including oscillators incorporating electronicsemiconductors, I may mention the simplicity of execution both for theoscillator and for the modulator as no particular shape is required forthe pips except for the straight edge of the sudden voltage that isimpressed on them, together with the very low wear of the arrangementand its consequently very long life.

Obviously, the diagrams and forms of execution described have been givenout solely by way of examples and by no means in a limiting sense whiletheir shapes and details of design or constitution may vary to aconsiderable extent without unduly widening the scope of the inventionas defined in accompanying claims.

WhatI claim is:

1. An ultra high frequency pulse oscillator comprising, in combination ahigh voltage periodic pulse source producing pulses with a steep wavefront, a resonant circuit including, in series, a condenser, aninductance and a granular semiconducting body and means for causing saidcondenser to be charged by said pulse source and to be dischargedthrough said inductance in series with said granular semi-conductingbody, said granular semi-conducting body being made up of small grainsof a semi-conducting material held together by an insulating materialand having an electrical resistance decreasing with the increase of avoltage applied thereto, said decrease in said resistance occurringafter a very short time interval and persisting for a time much longerthan said time interval after the application of said voltage.

2. An ultra high frequency pulse oscillator in accordance with claim 1,wherein the high voltage periodic pulse source consists in adirectcurrent voltage source in series with an impedance and acondenser, combined with a spark gap enabling said condenser to bedischarged through a pulse transformer.

3. An ultra high frequency pulse oscillator in accordance with claim 1,wherein the condenser included in the resonant circuit is constituted bythe capacity between the two conductors of a coaxial double quarter wavecoaxial line and wherein the granular semiconducting body is of annularshape and is inserted between and in contact with said two conductor inthe central section of said line.

4. An ultra high frequency pulse oscillator in accordance with claim 1,wherein the condenser included in a resonant circuit is constituted bythe capacity between two concentric hemispherical conductors and whereinthe granular semiconducting body is inserted between and in contact withsaid two conductors in the vicniity of their apices.

5. An ultra high frequency pusle oscillator in accordance with claim 1,wherein the condenser included in the resonant circuit is constituted bythe capacity between two conducting parallel plates and wherein thegranular semi-conducting body is inserted between and in contact withsaid plates in the vicinity of their central'parts.

6. An ultra high frequency pulse oscillator comprising, in combination,a high voltage periodic pulse source producing pulses with a steep wavefront, a resonant circuit including, in series, a condenser, aninductance and a granular semiconductor body and means for causing saidcondenser to be charged by said pulse source and to be dischargedthrough said inductance in series with said granular semi-conductingbody, said granular semi-conducting body being made up of small grainsof silicon carbide held together by an insulating material.

7. An ultra high frequency pulse oscillator in accordance with claim 6,wherein the high voltage periodic pulse source consists in adirect-circuit voltage source in series with an impedance and acondenser, combined with a spark-gap enabling said condenser to bedischarged through a pulse transformer.

8. An ultra high frequency pulse oscillator in accordance with claim 6,wherein the condenser included in the resonant circuit is constituted bythe capacity between the two conductors of a coaxial double quarter wavecoaxial line and wherein the granular semi-conducting body is of annularshape and is inserted between and in contact with said two conductors inthe central section of said line.

9. An ultra high frequency pulse oscillator in accordance with claim 6,wherein the condenser included in the resonant circuit is constituted bythe capacity between two concentric hemispherical conductors and whereinthe granular semiconducting body is inserted between and in contact withsaid two conductors in the vicinity of their apices.

10. An ultra high frequency pulse oscillator in accordance with claim 6,wherein the condenser included in the resonant circuit is constituted bythe capacity between two conducting parallel plates and wherein thegranular semi-conducting body is inserted between and in contact withsaid plates in the vicinity of their central part.

STANISLAS TESZNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,792,781 Thilo Feb. 17, 19311,949,383 Weber Feb. 27, 1934 2,487,279 Stalhane Nov: 8, 1949

